Flashcards in C2 1-8 Deck (37):
The structure of the earth
1. The crust
2. The mantle
3. The core
How do scientists study the structure of the earth?
Through seismic waves produced by earthquakes or explosions
What is the lithosphere?
The crust and the outer part of the mantle
What are tectonic plates?
The lithosphere is broken up into huge parts called tectonic plates. These float on top of the mantle because they are less dense.
How do earthquakes occur?
Earthquakes happen because of the movements of tectonic plates. Volcanic activity happens where the plates meet. Molten rock or magma gets to the surface through weak spots in the crust. The magma can rise through the crust because it is less dense than the crust.
What is the theory about plate tectonics?
The mantle is quite cold and rigid near the crust. Deeper down, the mantle becomes hotter and less rigid, and it flows slowly. Huge convection currents are set up. Hot material flows upwards, cools near the crust, then sinks again. These currents push the tectonic plates around the Earth.
What is subduction?
The oceanic plates are denser than the continental plates. If they collide with a continental plate, the cooler oceanic plate is pulled under the continental plate. The subducted oceanic plate partially melts and volcanoes can occur. It can create mountains too.
What was Alfred wegeners theory about continental drift?
He noticed that the shapes of the continents fitted together. He suggested that the continents were all once joined together, then gradually moved apart. Unfortunately, Wegener was unable to explain how continents could move.
Why did scientists believe Alfred wegeners theory later?
Scientists discovered convection currents in the mantle. They discovered evidence that tectonic plates were moving apart under the Atlantic Ocean, leading to sea-floor spreading, and they discovered subduction.
How is igneous rock formed?
When molten rock cools down, either underground or above ground, it solidifies to form igneous rock.
Why does igneous rock have different sized crystals?
The size of the crystals in an igneous rock depends upon the rate of cooling. The more slowly the molten rock cools, the larger the crystals become.
How are basalt and rhyolite different?
Basalt is iron-rich and forms from runny lava. This flows steadily and is regarded as relatively safe. Rhyolite is different. It is silica-rich and forms from thick lava. This explodes out of the volcano, producing lava bombs and volcanic ash.
How are metals, glass and bricks created?
aluminium and iron are metals extracted from metal ores. Bricks are made by baking clay, and glass is made by heating sand to very high temperatures.
What is a quarry?
a large but shallow hole in the ground, where large amounts of the desired rock can be found. Explosives are usually used to break up the rock so that it can be removed.
Why is limestone useful?
a lot of it is tough enough to be used as a construction material. Limestone can be cut into blocks, rather like large bricks, to make buildings. It can also be crushed to make aggregate. Aggregate is used as a firm base underneath railway lines, and as the foundation for roads before the tarmac is laid over the top.
What are the benefits of quarries?
- They provide jobs. This helps local families, and also shops and schools.
- The products from the quarries are valuable, and have many uses. This helps the country’s economic success.
What are the problems with quarries?
- often sited in attractive areas such as national parks. This may damage the tourist industry.
- Quarries are noisy and dusty, and so may affect the quality of life for local people.
- Using lorries to carry the rocks from the quarry to the customers produces extra traffic, which may have to pass through small towns or villages.
- Quarries take up land space, making it unavailable for other uses such as farming and recreation. They destroy the original landscape, so this must be restored when the quarry closes.
What is sedimentary rock?
Rock formed from the shells and skeletons of sea creatures
What happens when calcium carbonate is heated strongly?
It breaks down to form calcium oxide and Carbon dioxide.
CaCo3 -> CaO + Co2
What is thermal decomposition?
It is a reaction in which one substance is chemically changed, when heated, to produce two or more new substances.
How is calcium hydroxide formed and how can it be used?
calcium oxide + water → calcium hydroxide
Calcium hydroxide is an alkali. It can be used to neutralise acids. For example, farmers may spread it on their elds to reduce excess acidity in the soil, helping the crops to grow. It may also be used to treat lakes damaged by acid rain.
How is cement made?
Cement is made by heating powdered limestone with clay.
How is mortar made and what does it do?
Cement is mixed with sand and water to make mortar. This is the mixture used by bricklayers to stick bricks together. As it sets, it absorbs carbon dioxide from the air, forming tiny crystals of calcium carbonate, which lock together with the other ingredients.
How is concrete made?
Cement is mixed with sand, aggregate, and water to make concrete. This is the tough construction material that is widely used in buildings, bridges, and other man-made structures.
What is reinforced concrete?
Concrete can be strengthened by letting it set around a supporting mesh of solid steel. Such reinforced concrete is a composite material.
It has useful properties from both the materials it contains:
• concrete is hard and strong in compression (when
• steel is flexible and strong in tension (when stretched).
Benefits of copper
Copper is a valuable metal with properties that make it very useful. It is a good conductor of heat and electricity. Copper is ductile, which means it is easily made into wires. It is unreactive compared with most metals, which makes it useful for water pipes.
How do you purify copper?
using electrolysis, which involves passing an electric current through copper(II) sulfate solution.
Describe what happens during electrolysis
During electrolysis, copper is deposited and the cathode gains mass:
Cu2+ + 2e– → Cu (reduction)
The positively charged electrode, the anode, is impure copper. During electrolysis, copper dissolves and it loses mass:
Cu – 2e– → Cu2+ (oxidation)
This is an example of oxidation because electrons are lost.
What is an alloy?
a mixture of two or more elements, at least one of which is a metal.Alloys are often stronger and harder than the metals they contain.
What are shape memory alloys?
They are ‘smart alloys’. If they are bent out of shape, they return to their original shape when they are warmed. For example, a shape-memory alloy called nitinol is used for spectacle frames.
What is corrosion?
It happens when metals react with substances in the surroundings, such as air or water.
Why does aluminium not corrode easily?
Its surface is protected by a very thin natural layer of aluminium oxide. This layer is tightly bound to the metal and does not flake off. It stops air and water getting to the metal itself.
What happens when iron reacts with oxygen and water?
Iron is oxidised to hydrated iron(III) oxide when it reacts with oxygen and water:
iron + oxygen + water → hydrated iron(III) oxide
Similarities and differences in aluminium and iron
They are both
• good electrical conductors.
However, iron corrodes easily but aluminium does not. Iron
is also more dense than aluminium.
Iron is a magnetic material. On the other hand aluminium is not a magnetic material.
What are cars made of?
steel may be used for the car body, aluminium for the engine block, and copper for the electrical wiring. Glass is used for the windows, and plastic is used for the bumpers and dashboard. Fibres are used for the carpet and seat fabric.
Why is aluminium sometimes used for car bodies rather than steel?
Aluminium has a lower density than steel. A car body will weigh less if made from aluminium rather than steel. This should help the car to have a better fuel economy. Aluminium does not corrode in moist conditions, but steel will rust unless it is protected with paint and other coatings. But aluminium is more expensive.